1. Field of the Invention
The present invention relates to a driving structure and more particularly to a driving structure for a wheel hub of a bicycle.
2. Description of Related Art
Bicycle activity is more and more popular in the 21st century because bicycle activity is eco-friendly, convenient and entertaining. Many enterprises encourage their employees to go to work by bicycles instead of driving vehicles today. Many people also go shopping or go traveling by bicycles during their leisure time. Because a wheel hub of a bicycle is very important for the comfort of riding, a conventional driving structure for a wheel hub of a bicycle comes to the world.
The conventional driving structure for a wheel hub of a bicycle comprises a wheel hub and a ratchet base, the wheel hub having a ratchet wheel defined at one end thereof, the ratchet wheel having a plurality of teeth defined around an inner side thereof, the ratchet base having an operating member defined at one end thereof, the wheel hub connected to the ratchet base so that the operating member of the ratchet base is enclosed by the ratchet wheel of the wheel hub, a plurality of pivoting grooves defined around an outer periphery of the operating member, an engaging block having an engaging part and a pivoting part at two ends thereof, the engaging block pivoted on one end of each pivoting groove via the pivoting part, an elastic member being set into another end of each pivoting groove, the engaging part of the engaging block exposed from the pivoting groove toward the teeth of the ratchet wheel, the elastic member abutting against the engaging part so that the engaging part of the engaging block is engaged with the teeth of the ratchet wheel in only one direction.
Under this arrangement, when the ratchet base is clockwise rotated relative to the ratchet wheel of the wheel hub, the teeth of the ratchet wheel engage with the engaging parts of the engaging blocks because each elastic member abuts against the corresponding engaging block toward the teeth of the ratchet wheel. As a result, the wheel hub is rotated by the rotation of the ratchet base. In contrast, when the ratchet wheel of the wheel hub is clockwise rotated relative to the ratchet base, the teeth of the ratchet wheel disengage from the engaging parts of the engaging blocks because the engaging part is engaged with the teeth of the ratchet wheel in only one direction. As a result, the ratchet base is not rotated by the rotation of the wheel hub.
Therefore, when a user is riding, the wheel hub of the bicycle still rotates smoothly even though the user does not tread on a pedal of a bicycle.
However, the conventional driving structure for a wheel hub of a bicycle still has one disadvantage as following:
The recovery force of one elastic member might be different from the other elastic member so that the teeth of the ratchet wheel cannot simultaneously engage with the engaging parts of the engaging blocks when the ratchet base is clockwise rotated relative to the ratchet wheel of the wheel hub. Therefore, one engaging part which is always firstly engaged with the teeth of the ratchet wheel would be quickly broken.
The present invention has arisen to mitigate and/or obviate the disadvantages of the conventional. Further benefits and advantages of the present invention will become apparent after a careful reading of the detailed description with appropriate reference to the accompanying drawings.